The present invention relates to direct formation of dielectric thin films on silicon by low energy ion beam bombardment at room temperature.
Silicon dioxide is used in silicon MOS technology due to its excellent dielectric properties for use both for insulation and field enhancement in finished devices and at various stages of the fabrication process. Oxides for such applications are typically grown on the surfaces of silicon wafers at temperatures exceeding 900 degrees C. However, the requirements for increased performance and decreased dimension of semiconductor devices have necessitated the development of low-temperature fabrication processes such as ion implantation, rapid thermal annealing, and laser photochemical direct-writing processes. Reduced-temperature oxidation in thin-film FET's on low melting point substrates is desirable since repeated heating and cooling of the substrate leads to thermal stresses, crystal defects, wafer warpage and oxidation-enhanced diffusion which hinder the performance of small-dimension devices. These become increasingly important with the trend towards smaller device dimensions and efforts to fabricate stacked 3-dimensional MOS structures.
Various techniques have been proposed for oxidation of silicon at reduced temperatures, including plasma oxidation and anodization, chemical vapor deposition (CVD), plasma-enhanced CVD, photo-activated CVD, reactive sputtering, evaporation or sputtering in an oxygen ambient, and other methods. However, most of these processes have been applied to steps requiring a thick oxide and few of these have successfully produced thin oxides suitable for gate dielectrics. Presently high-temperature thermal oxidation remains the most viable means of producing high-quality gate dielectrics.
Ion beam oxidation has been used for oxidation of Nb using 600 eV oxygen ions to fabricate Josephson tunnel junctions. Low energy oxygen ion beams (45-80 eV) have been used in ion-beam oxidation of Ni and Cr and in reactive near-threshold sputtering of copper and silicon. In conjunction with photoelectron spectroscopy, a focused ion beam has been used to study oxidation kinetics on silicon (111).